1. Field
One embodiment of the invention relates to an encoding apparatus, an decoding apparatus, an encoding method, a decoding method, and an information recording and playback apparatus.
The present invention relates to an apparatus, method, an information recording and playback apparatus, and a recording medium of the same, which apply a modulation rule suitable for a recording medium to information to be recorded (user data), and adopt low-density parity check (LDPC) encoding and decoding method. For example, in magnetic recording, generally known modulation methods suitable for recording media are RLL encoding which limits the number of successive “0”, and MTR (Maximum Transition Run) encoding which limits the number of reversals of magnetization. The present invention is applicable to a recording and playback system adopting a modulation method such as RLL encoding and MTR encoding.
2. Description of the Related Art
Jpn. Pat. Appln. KOKAI Pub. No. 2005-78687 discloses a technique obtained by combining a technique of encoding a data word of m bits into an information word of n bits satisfying RLL rules, with a technique of LDPC encoding and decoding method. In the technique, check bit information of LDPC code is inserted into an information word string, and digital sum value (DSV) control is performed.
When information encoded by LDPC encoding and decoding method is decoded, correction and decoding are performed on the supposition that each bit is independent. Therefore, LDPC encoding and decoding method has a high correction ability for random errors and discrete errors. However, LDPC encoding and decoding method has a problem of having a weak correction ability for continuous errors. Such continuous errors occur in reproduced signals due to dust or scratches on a part of a recording medium.
To cover the weakness of LDPC encoding and decoding method, it is one choice to interleave LDPC codes when signals are recorded on a recording medium. The recorded interleaved signals are deinterleaved when they are played back. Therefore, continuous error parts are dispersed by deinterleave and changed into random errors, and thereby the correction ability of LDPC encoding and decoding method can be sufficiently exhibited. However, performing interleave causes the following new problem.
Specifically, when information is recorded on a recording medium, for example, RLL rule processing is performed for user data as modulation rule applying processing, and then LDPC encoding is performed for the processed data. Then, interleave processing is performed to compensate the weakness of LDPC encoding and decoding method.
The problem of the above process is that the RLL rule which has been applied to the data is damaged by the interleave processing. To avoid the above problem, the encoding order “LDPC encoding→interleave→RLL encoding” can be adopted. Adopting the above order enables obtaining of a transmission sequence without damaging the RLL rules.
However, there is a significant reason why LDPC encoding must be performed after RLL encoding. Specifically, in RLL codes and MTR codes, the value of input and output sequences is “0” or “1”. However, in “repeated decoding” used for LDPC codes and turbo codes, an input of a decoder is not a hard value such as “0” or “1”, but a probability value (soft value) representing the likelihood that the value is “0” or “1”. Therefore, also in PRML method, SOVA (Soft Output Viterbi Algorithm) which outputs a soft determination value and Max-Log-Map algorithm are used instead of a conventional Viterbi decoder which outputs a hard determination value as a maximum likelihood sequence. Therefore, sequences encoded in the order “LDPC encoding→interleave→RLL encoding” have to be decoded in the order “RLL encoding→deinterleave→LDPC encoding”. However, in this case, an input to the RLL decoder is a soft determination value, and thus it is difficult to perform RLL decoding. Further, if RLL decoding can be performed for the soft determination information, it is highly possible that the determination information includes many errors, and thus the performance of LDPC decoding is not fully exhibited.